1. Field of the Invention
The present invention relates to an image processing apparatus and an image processing method for adding information to detect falsification to document image data, a program executing the image processing method, and a medium storing the program.
2. Description of the Related Art
Nowadays, information security techniques to protect electronic data have been developed and applied on a daily basis.
For example, in Patent Document 1 (Japanese Patent Laid-Open No. 2003-051932), a technique of detecting abuse of a copyrighted specific image (e.g., a character image) is disclosed. This technique is implemented in a situation where, every time electronic data is created by using a specific image, a copyright notice mark is embedded in a predetermined area outside an area where the specific image exists. If electronic data including a specific image does not have a copyright notice mark in the predetermined area, the electronic data is determined to be unauthorized. In Patent Document 1, the predetermined area is defined as an area having a predetermined position relationship with an area where a specific image exists. Also, according to Patent Document 1, the predetermined area may be placed in the same page as the specific image or in a different page.
The information security technique is also applied to a paper document, having merits of high visibility and easy handling.
For example, a feature value embedding technique of generating a feature value (e.g., hash value) from a paper document and embedding the generated feature value in the paper document has been proposed. This technique is used to detect falsification in a paper document.
Also, a page sort technique disclosed in Patent Document 2 (Japanese Patent Laid-Open No. 10-228470) has been suggested for a paper document, although this technique does not involve information security. In the technique disclosed in Patent Document 2, page numbers are embedded in respective pages by watermarks. When a user processes a paper document embedded with page numbers on a copying machine, the copying machine extracts watermarks from the respective pages and recognizes respective page numbers. Then, the copying machine sorts the pages on the basis of the recognized page numbers and outputs a copy sorted in orderly sequence from a first page.
However, even if a paper document including a plurality of pages is created by embedding a feature value of each page in the page by using the feature value embedding technique, the paper document can be easily falsified and the falsification cannot be detected. For example, if someone discards one of the pages of the paper document, the fact that the page has been discarded may not be established. Also, if someone creates a page and adds it to the paper document or replaces a page in the document with the created page, the fact that the page has been added or replaced may not be established. That is, in this feature value embedding technique, the originality of each page can be proved, but the originality of the entire paper document including a plurality of pages cannot be proved.
Furthermore, even if a paper document including a plurality of pages is created by embedding watermarks in the respective pages by using the technique described in Patent Document 2, this watermark embedded paper document can be easily falsified and the falsification cannot be detected. For example, if someone rewrites an area that is not embedded with a watermark, the fact of the rewrite cannot be established.
Also, if a document is created by embedding a copyright mark in each page by using the technique described in Patent Document 1, this document can be easily falsified and the falsification cannot be detected. For example, if someone rewrites an area outside a specific image and the copyright mark, the fact of the rewrite cannot be established.
Under these circumstances, a technique of creating a document including a plurality of pages while guaranteeing its originality has been desired.
Herein, “falsification” means rewrite, replacement, pilferage, and so on. The “originality” means “authenticity”. An “originality-guaranteed document” means a document that is guaranteed of not being falsified.